The invention relates to a device for accommodating at least onexe2x80x94preferably electrical or electronicxe2x80x94component, comprising a housing, in the interior of which the at least one component is arranged, the interior of the housing being filled with a casting material.
It is known to use hot-melt adhesives for the production of moulded parts or for the sealing of plug connectors or as an encapsulating mass for electrical or electronic components. Thus, hot-melt adhesives have been employed, for example, for years for water-tight plug connectors. In addition, there are also special hot-melt adhesives on a polyamide base (for example, the product Macromelt (Registered Trade Mark) marketed by the applicant) which provide more than just a water-tight adhesion. Such an adhesive prevents, in particular, not only the ingress of moisture into the plug, but also imparts mechanical strength to the plug connector and fulfills further tasks which were previously fulfilled by additional, high-cost plastic parts. Hot-melt adhesives of this kind are based on, for example, polyamide and have a melt range from 120 to 180xc2x0 C. They adhere to many plastics, such as polyethylene, polyvinylchloride and polyamide, and have low viscosity. In one method used for injection moulding, the heated hot-melt adhesive is injected into a tool. The liquid melt is suitable for flowing around filigree components, even without high pressure, without impairing the function of the components. The adhesive penetrates into the smallest spaces even at a pressure between 5 and 10 bars. The low pressure has the consequence that the entire method is very economic, since the machine can be designed for this low loading. The tools can be produced favourably in cost from aluminium. This method is suitable for, for example, encapsulating cable passages or for wire insulation. The encapsulation of switches, plugs, contacts, sensors and other electronic components is equally possible and opens up a further field of use. Such a method can be used wherever electrical currents flow and sealing is necessary.
In principle it is possible to either fill a housing, in which the electronic component is arranged, with cast hot-melt adhesive or to produce the entire housing itself from hot-melt adhesive. However, such a housing consisting solely of hot-melt adhesive has only a low mechanical strength compared with a plastic material housing and accordingly can be used only in specific applications.
In the case of use of devices according to category with a plastic material housing and an internal filling of casting material consisting of hot-melt adhesive the problem arises, however, that under temperature change of the finished units the hot-melt adhesive detaches again from the housing wall so that the electronic component or components in the housing is or are no longer sealed. For this reason it has been usual in the past to injection-mould hot-melt adhesive completely externally around the housing. However, due to space considerations this is not always possible.
It is therefore the object of the invention to further develop a device according to category, with maintenance of the mechanical strength thereof, so that it is reliably sealed towards the outside even in the case of temperature changes.
According to the invention this object is met by a device of the kind stated in the introduction in the manner that the housing is provided at the inner side with at least one encircling projection having an undercut.
When filling the housing, which is furnished with at least one electronic component or the like, with casting material the casting material then also flows into the region between the housing inner wall and the encircling projection and is thereby, so to speak, self-locked to the housing. Even in the case of temperature change tests, i.e. extreme temperature changes, it is ensured that the casting material cannot detach from the housing inner wall, so that the device as a whole remains reliably sealed.
In that case it is then preferably provided that the projection is arranged in the centre region of the housing, so that the casting mass is then retained approximately symmetrically in the housing.
As known per se, the casting material can with particular advantage consist of hot-melt adhesive on a polyamide base. Preferably there can then be used an adhesive placed on the market by the applicant under the designation Macromelt (Registered Trade Mark). Alternatively, other hot-melt adhesives, for example on a polyurethane or polyester base, can also be advantageously used.
If the housing is to be injection-filled with the casting material the housing advantageously has at least one injection bore for the casting material in the region of the projection. The injection bore then penetrates the projection which, however, is otherwise formed to be encircling.
The projection is Connected with the outer wall of the housing in rigid manner it the projection encircles continuously and is connected with the outer wall of the housing by means of a strut- or bridge-like connecting wall. In that case, it is preferably farther provided that the projection and connecting wall are together formed to be cross-sectionally T-shaped.
In a particularly preferred development the invention further provides that the projection encircles in sections and is connected with the outer wall of the housing by means of a respective connecting wall for each section. This enables particularly good flowing of the bonding material into the gap between the projection and the outer wall and prevents bubble formation in the region behind the undercutting of the projection. In addition, this enables production of the housing of the device according to the invention in a plastic injection moulding process with uniform wall thicknesses without the risk of shrink holes in the internal surface of the housing.
Finally, as also provided by the invention it is of particular advantage in the case of this embodiment if the connecting wall is formed to be circular in each section.